I am looking into an issue of hanging clients to a set of NFS servers, on
a large HPC cluster.
My investigation took me to the RPC code, svc_create_socket().
if (protocol == IPPROTO_TCP) {
if ((error = kernel_listen(sock, 64)) < 0)
goto bummer;
}
A fixed backlog of 64 connections at the server seems like it could be too
low on a cluster like this, particularly when the protocol opens and
closes the TCP connection.
I wondered what is the rationale is behind this number, particuarly as it
is a fixed value. Perhaps there is a reason why this has no effect on
nfsd, or is this a FAQ for people on large systems?
The servers show overflow of a listening queue, which I imagine is
related.
$ netstat -s
[...]
TcpExt:
6475 times the listen queue of a socket overflowed
6475 SYNs to LISTEN sockets ignored
The affected servers are old, kernel 2.6.9. But this limit of 64 is
consistent across that and the latest kernel source.
Thanks
--
Mark
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